Flat-panel display devices are widely used in conjunction with computing devices, in portable devices, and for entertainment devices such as televisions. Such displays typically employ a plurality of pixels distributed over a substrate to display images. Each pixel incorporates several, differently colored, light-emitting elements commonly referred to as sub-pixels, typically emitting red, green, and blue light, to represent each image element. A variety of flat-panel display technologies are known, for example plasma displays, liquid crystal displays, and light-emitting diode displays.
Light emitting diodes (LEDs) incorporating thin films of light-emitting materials forming light-emitting elements have many advantages in a flat-panel display device and are useful in optical systems. U.S. Pat. No. 6,384,529 issued May 7, 2002 to Tang et al. shows an organic LED (OLED) color display that includes an array of organic LED light-emitting elements. Alternatively, inorganic materials can be employed and can include phosphorescent crystals or quantum dots in a polycrystalline semiconductor matrix. Other thin films of organic or inorganic materials can also be employed to control charge injection, charge transport, or charge blocking to the light-emitting-thin-film materials, and are known in the art. The materials are placed upon a substrate between electrodes, with an encapsulating cover layer or plate. Light is emitted from a sub-pixel when current passes through the light-emitting material. The frequency of the emitted light is dependent on the nature of the material used. In such a display, light can be emitted through the substrate (a bottom emitter) or through the encapsulating cover (a top emitter), or both.
LED devices can comprise a patterned light-emissive layer wherein different materials are employed in the pattern to emit different colors of light when current passes through the materials. Alternatively, one can employ a single emissive layer, for example, a white-light emitter, together with color filters for forming a full-color display, as is taught in U.S. Pat. No. 6,987,355 entitled, “STACKED OLED DISPLAY HAVING IMPROVED EFFICIENCY” by Cok. It is also known to employ a white sub-pixel that does not include a color filter, for example, as taught in U.S. Pat. No. 6,919,681 entitled, “COLOR OLED DISPLAY WITH IMPROVED POWER EFFICIENCY” by Cok et al. A design employing an unpatterned white emitter has been proposed together with a four-color pixel comprising red, green, and blue color filters and sub-pixels and an unfiltered white sub-pixel to improve the efficiency of the device (see, e.g. U.S. Pat. No. 7,230,594 issued Jun. 12, 2007 to Miller, et al).
Two different methods for controlling the pixels in a flat-panel display device are generally known: active-matrix control and passive-matrix control. In an active-matrix device, control elements are distributed over the flat-panel substrate. Typically, each sub-pixel is controlled by one control element and each control element includes at least one transistor. For example, in a simple, prior-art active-matrix organic light-emitting (OLED) display, each control element includes two transistors (a select transistor and a power transistor) and one capacitor for storing a charge specifying the brightness of the sub-pixel. Each light-emitting element typically employs an independent control electrode and a common electrode.
A wide variety of technologies are employed for integrating computing circuitry. Integrated circuits formed on silicon substrates and packaged in ceramic or plastic packages have been used for many years. Wires extending from the top of the silicon substrate are bonded to pins to provide electrical connectivity to the circuits. Other packaging methods are known, for example flip chips, in which the silicon substrate is bonded to another substrate with electrically-connective solder bumps. Multi-Chip-Modules incorporating multiple silicon substrates in a common package are also used to increase packaging density. These technologies are described, for example, in “The Electronic Packaging Handbook”, copyright 2000, Ed. Blackwell, ISBN-10 0849385919, published in collaboration by CRC Press and IEEE Press. Three-dimensional chip stacks are also known, in which bare die are interconnected to form stacks of computing elements.
One common, prior-art method of forming active-matrix control elements typically deposits thin films of semiconductor materials, such as silicon, onto a glass substrate and then forms the semiconductor materials into transistors and capacitors through photolithographic processes. The thin-film silicon can be either amorphous or polycrystalline. Thin-film transistors (TFTs) made from amorphous or polycrystalline silicon are relatively large and have lower performance compared to conventional transistors made in crystalline silicon wafers. Moreover, such thin-film devices typically exhibit local or large-area non-uniformity across the glass substrate that results in non-uniformity in the electrical performance and visual appearance of displays employing such materials.
Photo-voltaic systems that generate electricity also employ silicon films, either crystalline or amorphous, together with transparent and metallic conductors.
Matsumura et al describe crystalline silicon substrates used for driving LCD displays in US Patent Application No. 2006/0055864. The application describes a method for selectively transferring and affixing pixel-control devices made from first semiconductor substrates onto a second planar display substrate. Wiring interconnections within the pixel-control device and connections from busses and control electrodes to the pixel-control device are shown.
It is useful to test devices during manufacture to identify faulty devices as soon as possible. By identifying the faulty devices, the devices can be repaired or rejected without doing further work on the faulty device and thereby wasting manufacturing resources. It is difficult, however, to test pixel-control circuits for displays without actually constructing the displays and observing the light emission from the displays. At that point in the manufacturing process, it can be impossible to correct a circuit defect and the device must be discarded. There is a need, therefore, for an improved manufacturing process for constructing a device that is amenable to repair in the presence of manufacturing faults. Furthermore, there is a need for improved control circuits with higher performance distributed over a substrate.